1. Technical Field
The present invention relates to an angular velocity sensor.
2. Background Art
Angular velocity sensors have been traditionally used, for example, in controlling the attitude of such mobile units as aircraft, vehicles and the like and in navigation systems, and the like. Such conventional angular velocity sensors are described in the Japanese Patent Application Unexamined Publication No. H8-271257.
A description is given below to conventional angular velocity sensors with reference to drawings.
FIG. 11 is a side cross-sectional view of a conventional angular velocity sensor and FIG. 12 and FIG. 13 are a top cross-sectional view and a bottom view of the same, respectively.
In FIG. 11 to FIG. 13, a tuning fork (resonator) is fixed on a first base 1. The tuning fork comprises a first resonating member (not shown in drawings) and a second resonating member (not shown in drawings). First base 1 has three terminal insertion holes (not shown in drawings). Three terminals 2 are inserted in three respective terminal insertion holes (not shown in drawings). A driving electrode (not shown in drawings) or a detecting electrode (not shown in drawings) is disposed on first and second resonators. Three terminals 2 are electrically connected to the driving electrode or the detecting electrode. Cover 3 is put in place to cover the tuning fork fixed onto first base 1. First circuit board 4 holds securely terminal 2 protruding from first base 1 by soldering. Thus, first base 1 and cover 3 with the tuning fork housed inside thereof are put together. Second circuit board 5 is disposed almost in parallel to first circuit board 4. Electronic device 6 for processing an output signal produced at the detecting electrode of the tuning fork in accordance with an angular velocity is mounted on the surface of second circuit board 5. On second circuit board 5 are disposed a power supply electrode (not shown in drawings), a GND electrode (not shown in drawings) and an output electrode (not shown in drawings). These electrodes are electrically connected to respective three terminals 2 mounted on first base 1 via first circuit board 4 and conductor 7. A pair of rubber pieces 8 hold the side surfaces of circuit board 4. First base 1, cover 3, first circuit board 4, second circuit board 5 and a pair of rubber pieces 8 are housed inside of bottomed cylindrical case 9. A pair of holding members 11 protrude upward from respective both end parts of resin made second base 10 to hold the pair of rubber pieces 8. An opening of case 9 is closed by second base 10. On second base 10 are disposed three external terminals 12, which protrude downward therefrom. These external terminals 12 are electrically connected to the power supply electrode (not shown in drawings), GND electrode (not shown in drawings) and output electrode (not shown in drawings) that are disposed on second circuit board 5, respectively.
Next, a description is given to how the conventional angular velocity sensor structured as above performs.
An alternating voltage is applied to the driving electrode of the tuning fork (resonator), thereby causing the tuning fork to vibrate by bending in the driving direction at a velocity of V with a natural frequency of vibration in the driving direction. When the tuning fork rotates at an angular velocity of xcfx89 around the center axis thereof under this state, a Coriolis force of F=2 mV. xcfx89is generated on the first resonating member and second resonating member of the tuning fork, respectively, thereby allowing the electric charges produced on the detecting electrode to be fed to electronic device 6 mounted on second circuit board 5 via first circuit board 4 and conductor 7. An output voltage amplified in electronic device 6 is supplied as an output to an external computer and the like via external terminal 12. Thus, an angular velocity is allowed to be detected.
According to the conventional set-up as described in above, however, a pair of rubber pieces 8 are held by a pair of holding members 11 disposed on second base 10 and first circuit board 4 is fixed so as to have rubber piece 8 compressed by holding member 11. Since holding member 11 produced by resin molding has inherently a wide range of variation in dimensions, rubber piece 8 presents a variation in compressibility, resulting in changes of vibration applied from outside to the tuning fork, which is housed inside cover 3, via rubber piece 8 and first circuit board 4. Therefore, the output characteristics of the angular velocity sensor end up with being made unstable.
The present invention is to provide an angular velocity sensor with stabilized output characteristics realized by preventing a variation in compressibility of rubber pieces.
An angular velocity sensor of the present invention comprises:
(a) a resonator including a resonating member and a connecting member;
(b) a first base connected to the connecting member;
(c) a holding plate to hold the first base;
(d) a circuit board fixed onto the holding plate;
(e) an elastic body disposed on an end part of at least one selected from the holding plate and circuit board; and
(f) a case having an opening and accommodating the resonator, first base, holding plate, circuit board and elastic body,
wherein the elastic body is located between the inner walls of the case and an end part of at least one selected from the holding plate and circuit board; and
at least one selected from the holding plate and circuit board is held by the case with elastic pressure of the elastic body.
Preferably, the angular velocity sensor further comprises:
(g) a second base put in place so as to close the opening of the case, wherein the resonator has a short side and a long side; and
the resonator is located on the second base so as to have the long side thereof directed perpendicular to the surface of the second base.
A manufacturing method of angular velocity sensors of the present invention comprises the steps of:
(a) producing a resonator that includes a resonating member and a connecting member;
(b) producing a first base;
(c) producing a holding plate;
(d) producing a circuit board;
(e) producing an elastic body;
(f) producing a case;
(g) connecting the connecting member of the resonator to the first base;
(h) having the circuit board held on the first base;
(i) fixing the first base onto the holding plate
(j) putting together the resonator, holding plate, circuit board and elastic body in such a way that an end part of at least one selected from the holding plate and circuit board is held by the elastic body; and
(k) disposing the assembly formed of the resonator, first base, holding plate, circuit board and elastic body in the case so as to have the resonator and circuit board situated inside of the case via the elastic body.
Preferably, the manufacturing method further comprises the step of
(l) producing a second base,
wherein the resonator has a short side and a long side,
the step (j) has a step of putting together the resonator, first base, holding plate, circuit board, second base and elastic body so as to have an end part of at least one selected from the holding plate and circuit board held by the elastic body, and
the step (k) has a step of pressing into the case the assembly formed of the resonator, first base, holding plate, circuit board, second base and elastic body so as to have the long side of the resonator directed perpendicular to the second base and another step of having the opening of the case closed with the second base so as to have at least one selected from the holding plate and circuit board held by the case.
Preferably, the step of producing the resonator has a step of producing a resonator that includes a first resonating member, a second resonating member, a driving electrode and a detecting electrode,
wherein respective end parts of the first resonating member and second resonating member are connected to the connecting member, and
the driving electrode and detecting electrode are disposed on at least one selected from the first resonating member and second resonating member.
Accordingly, a variation in compression rate of an elastic body is prevented, thereby making an angular velocity sensor with stable output characteristics available.